On Monday 10 March 2014 17:30:25 John Kasunich did opine: > On Mon, Mar 10, 2014, at 04:55 PM, Gene Heskett wrote: > > Continuing this thread of trying to determine what belt I need to > > properly fit these pulleys, I have talked to Chris Wood at LMS but he > > can't help me with anything but OEM parts, so some math based on the > > gullet od + the tip od on the pulley, half of that to get the "pitch > > diameter" converted to pitch circumference, then divided by the > > number of cogs, 30 in this case, give me a pitch length of 4.60mm, > > and in cycling my digital caliper through its modes, one thing seems > > to stand out, 3/16". Are there belts made with a 3/16" pitch? > > On most timing belts, the "pitch line" (where you measure pitch > diameter) is not half-way up the teeth as you calculated. It is > actually a little outside the tops of the teeth, where the strength > members of the belt are. See the drawing at > http://ca-cycleworks.com/c/pics/machining/tb_meas/Timing_Belt_Pulley_Pit > ch_Diameter_and_Outside_Diameter.jpg
Oh goody. And of course its an imaginary line you can't put a caliper on. Loverly, just fscking loverly. From the looks of that drawing, one would add perhaps about half the thickness of the belt measured in the center of the cup separating the cogs. That would make the pitch line 1.3mm taller (in diameter) than the peak of the tooth. That would be about 45.84mm + 1.3mm added only once to get the solid line shown. Thats 47.15mm, fed into a circumference calculator returns 148.12609361675874 for pitch circumference, divided by the teeth, 30=4.937536453891958mm. But this miss fit belt is stamped 1.5x70. Its cogs do NOT begin to fill the gullies of the pulley. I am thinking a 5mm belt might be a closer fit. But those all appear to be a full 10mm wide, just a black one too wide for the flanges on the driving pulley. The now worn one is about 9.75mm between the flanges at the root of the gully, and only 9.85 at the top of a cog. But lets work it backwards from 30 teeth 5mm pitch. That is 150mm pitch circumference. Continuing backwards that is still within the cross sectional web of the belt so its possible. So I need a 74 cog 5mm pitch belt 9.5mm wide. Am I at least in the ballpark? I need a beer. 2 maybe. Its turning into a headache... :( Thanks John & Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Learn Graph Databases - Download FREE O'Reilly Book "Graph Databases" is the definitive new guide to graph databases and their applications. Written by three acclaimed leaders in the field, this first edition is now available. Download your free book today! http://p.sf.net/sfu/13534_NeoTech _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
